This invention relates to electrical switch apparatus of the electro-mechanical type, and more particularly to a switch apparatus suitable for use in circuit breaker applications.
Circuit breakers commonly used for protecting an electrical wiring network from current overloads and short circuits typically include a mechanical switch which is normally closed but which is opened when a tripping mechanism in the circuit breaker senses a current exceeding a predetermined limit. Because the circuit breaker switch is opened while current is flowing between its contacts, an arc discharge generally occurs between the contacts when they are initially separated. Such an arc discharge generates a plasma in the region adjacent to the switch contacts and causes current conduction through the switch to continue after the contacts are separated until the discharge is extinguished. The duration of the arc discharge after contact separation depends upon such factors as the voltage across the switch and whether the current carried by the switch is AC or DC. The occurrence of the arc discharge in a circuit breaker switch is undesirable in that it slows the response of the circuit breaker to an overload condition and tends to shorten the life of the contacts. Therefore, switches used in circuit breakers commonly include provisions for extinguishing such arc discharges.
FIG. 1 shows a cross-sectional view of a conventional configuration for a circuit breaker switch. The switch includes a terminal screw 5, a fixed contact electrode 3, a movable contact electrode 8, a fixed conducting member 1 connecting the terminal screw 5 to the fixed contact electrode 3, a movable conducting member 7 connecting the movable contact electrode 8 to another terminal screw, which is not shown, and a tripping mechanism, which is also not shown, for selectively bringing the fixed and movable contact electrodes into contact under normal conditions and for automatically separating the contacts when the current limit for the circuit breaker is exceeded.
The fixed member 1 is depicted in an isometric view of FIG. 2, in which the same reference numerals used in FIG. 1 are used to denote the same portion and features of that component. The fixed member is formed from a strip of metal bent into the shape illustrated and has a tapped hole near one end thereof for receiving the terminal screw. A contact electrode 3 made from a suitable contact material is affixed, as by brazing, near the other end of the strip.
Referring again to FIG. 1, when the contact electrodes 3 and 8 of the switch are separated while a current is flowing in the switch, an arc discharge is struck between the electrodes generating a plasma in an arc zone, which is partially represented by the stippled region 9. Such an arc discharge gives rise to current conduction in the switch after separation of the electrodes. In order to extinguish the arc discharge, there is provided arc extinguishing means in the form of a plurality of grid members 12 made of a magnetic material and placed in close proximity to the aforementioned arc zone. The grid members are enclosed within a chamber 11 formed by insulating walls 13 on three sides of the grid members.
The chamber and grid members are illustrated in an isometric view of FIG. 3, in which the same reference numerals used in FIG. 1 are again used to denote the same features of those components. The grid members are planar and "C" shaped and are positioned in parallel at regular intervals along vertical direction within the chamber. The chamber 11 is open on one side to be in communication with the arc zone. The portion of arc discharge plasma, which enters the chamber and comes into contact with the grid members, is dispersed and cooled thereby. If the plasma in the arc zone becomes sufficiently cooled and dispersed by the grid members, the discharge is extinguished.
Referring again to FIG. 1, a deficiency of the conventional switch configuration is that as the current and/or voltage carried by switch is increased, the extent of the arc zone in the switch tends to become larger. Consequently, in a switch designed for high capacity applications, i.e., for carrying a high current and/or voltage, the chamber 11 must be made larger and the arms of the "C" shaped grid member must be made longer in order to provide sufficient cooling and dispersal of a more extensive plasma to cause rapid extinguishment of the discharge. However, the use of the larger chamber and longer grid members results in a switch construction which is undesirably large and costly to manufacture. Therefore, a need exists for a switch configuration for high capacity application which provides rapid extinguishment of an arc discharge during switch opening and has a construction which is more compact and less costly to manufacture.